1. Field of the Invention
The present invention relates to an image coding apparatus and an image coding method. More specifically, the present invention relates to, for example, a method suitable for control of coding of a picture when a flash unit emits light.
2. Description of the Related Art
Conventionally, a Moving Picture Experts Group (MPEG) coding method performs intra coding and inter coding. In the intra coding, information within a picture is used. In the inter coding, an inter-picture difference is used. In the inter coding, a difference between a picture to be encoded and a reference picture is encoded.
In coding processing, a code amount allocated to a picture is determined based on a given rate, and further, an amount of target code provided to one macroblock is computed based on the determined code amount. Based on the amount of target code provided to the macroblock, a quantization coefficient is determined, and quantization is performed based on the determined quantization coefficient (see Japanese Patent Application Laid-Open No. 2003-102007).
An imaging apparatus mounted with an MPEG coder-decoder (MPEG codec) is already in the market. In connection with the apparatus, Japanese Patent Application Laid-Open No. 2001-025011 discusses a method of controlling of coding according to information of a shutter speed.
However, in the above conventional methods, for example, coding control is not described which is suitable for taking a picture when a flash unit emits light.
For example, in the case of using an MPEG codec in an imaging apparatus, a flashing unit for shooting a still image can flash during shooting of a moving image. In addition, during shooting of a moving image, a flashing unit of another camera, which is shooting the same object, can emit light at the same time. In these cases, a rapid luminance change of the photographed object occurs.
Therefore, in encoding a video signal obtained by shooting the object, the video signal can be adversely affected by the flashing of a flash unit. More specifically, an encoding device cannot appropriately respond to the luminance change of a video image for a certain length of time when the rapid luminance change has arisen due to the flashing. Accordingly, an efficiency of coding is lowered, and an image quality deteriorates.